So the reason why Zulip doesn't use React for the web app is that there was no React(at least not available for public) when Zulip started out in 2012. The Javascript frameworks which did exist in 2012 no longer exists or is not used by anyone anymore. Zulip still uses jQuery with some internal abstractions. The reason why Zulip decided to use React Native for mobile app was probably it was much easier to have a single codebase than maintaining a different codebase for Android and iOS. Same reason for using Electron for Desktop app. That said we have been talking about the possibility of using a Javascript framework for Zulip web app for a while now but we have not found a good enough reason to make the switch yet. See the following link for more details https://chat.zulip.org/#narrow/stream/6-frontend/topic/vue.2...